NEOPROTEROZOIC WESTERN U.S.:
These
projects focus on mid- to late Neoproterozoic strata and their
implications for global paleoclimate, regional tectonics, ocean
geochemistry, and correlation.

Jaking the Red Castle Formation, High Uintas (left). Carrying
samples out of the Uintas with help from Thomas and Sonny the llamas.
Kings Peak, highest peak in Utah, on skyline (right).

NEOPROTEROZOIC UINTA MOUNTAIN GROUP, UTAH AND COLORADO

The
Uinta Mountain Group(UMG) is an amazingly understudied, 4-7
km thick succession of newly dated Proterozoic
strata. U-Pb analyses on detrital zircons has revealed a maximum
depositional age of 766 Ma (Fanning and Dehler, 2005). Therefore, the
UMG correlates
to other dated Neoproterozoic successions in the western U.S. such as
the Chuar Group.
Ongoing research in the western Uintas is focused on the Red Pine
Shale--an
organic-rich shale sequence (TOC)>6%). These rocks are
amenable
to chemostratigraphic analyses (on organic carbon) and a detailed
C-isotope
curve has been generated for about 1000 m of this unit. More
traditional
stratigraphic and sedimentologic studies are also underway --this unit
has
not been thoroughly described and paleoenvironmental interpretations
remain
controversial. Correlative(?) strata on the eastern side of the
range
are very different and we (me and students) hypothesize that the UMG in
this area represents 4-7000 m of braided stream and marginal marine
deposition.
Mapping in the eastern UMG by students has resulted the
subdivision into formations, and sequence stratigraphic
principles may be applicable. We also hypothesize (me and Doug
Sprinkel
from the UGS) that the eastern UMG correlates with the units to the
west
(e.g., Red Pine Shale), but years of mapping will be necessary to test
this. Strata in the Kings Peak area in the central part of the
range is amenable to sequence stratigraphy and will help to test this
hypothesis.
Photo to left: Typical outcrop of the eastern UMG (braided stream deposits). Bushes are ~ 1 m tall.

Photomicrograph to right (2.5X): Typical
quartz arenite in the eastern Uinta Mountain Group.
That's right, much of this Precambrian unit is NOT quartzite, but simply a well cemented sandstone.

Above: Dan Rybczynski in his map area near the type section of the new formation of Outlaw Trail, eastern Utah.

CHUAR GROUP--NEOPROTEROZOIC RECORD OF THE GRAND CANYON AREA

This
research
project was part of a larger, NSF-funded project designed to answer
large-
and small-scale questions about the Neoproterozoic history of the
Southwestern
US and beyond. The Chuar Group is a postage stamp of an outcrop
belt (150 km2), but is one of the few unmetamorphosed successions of
this
age. The focus of my PhD project was to characterize and interpret
the
Chuar Group in terms of depositional environments and basin style, as
well
as climate and ocean geochemistry. Conclusions of this work reveal
large-scale
C-isotope shifts in organic and carbonate carbon. These shifts
coincide
with lithostratigraphic and shale geochemical data and the combined
datasets (see below) suggest that climate control was a player for the
C-isotopic variability.
This is significant when considering the age of the Chuar Group
(>742
Ma) and how it may be coeval or precursory to global-scale
glaciations.
See Karlstrom et al, 2000, Porter and Knoll, 2000; Dehler et al, 2001;
Timmons
et al., 2001, Dehler et al., 2005 for more information. Research on this amazing unit continues.

Figure to left: The
generation and comparison of multiple datasets collectively
indicate climate as a control on the carbon cycle in the
mid-Neoproterozoic (see Dehler et al., 2005, GSAB)

Photo to right: The Jupiter and Carbon Canyon members of
the Chuar Group, ~400 m in view.
Are these strata hot or what?

Photo to left: The "brain bed"--complex stromatolites often
referred to as Baicalia or Boxonia. Note the intimate
relationship with variegated siliclastic shale. These microbial
buildups likely grew when climate was dryer and sea level was
relatively lower (and there was more glacial ice on the planet).
See Dehler et al., 2001 for reasoning..

Photo to right: Meter-scale
cycles in the Carbon Canyon Member of the Chuar Group,
interpreted to
be glacioeustatic. See Dehler et al., 2001.

Photo to left: The Sixtymile Formation unconformably
overlies the Chuar Group. Note paleovalley--is this a record
of sea-level drawdown due to glaciation during the late Neoproterozoic (Sturtian)?

OTHER NEOPROTEROZOIC RESEARCH:

ChUMP
hypothesis (Chuar-Uinta Mountain-Pahrump groups).

This idea has been proposed
by many workers. Recent detailed
work on all three of these successions will allow testing
the idea that the Chuar, Uinta Mountain, and Pahrump groups, are, atleast
in part, correlative and were part of a western Interior Seaway in the Neoproterozoic.

Correlation of mid- to late Proterozoic deposits in Utah and Idaho.
NSF $ pending. The goal here is to answer questions about
the style and timing of the rifting of the western Laurentian margin.
This project will also address the timing and style of
glaciations during this time, and test the snowball Earth hypothesis.

C-isotope stratigraphy of the Toby cap carbonate. Emmanuelle
Arnaud and I are studying this cap carbonate to see if it is "like the
others"...

Paleoecology and the carbon cycle prior to the Sturtian glaciation.
Susannah Porter and I are looking at fossil and stratigraphic
data from mid-Neoproterozoic units to try and understand the cause(s)
for ensuing low-latitude glaciations.

The
photomicrograph on the left is from a rock sample known to have been
quarried by Paleoindians. The photomicrograph to the right is
from a quartzite artifact, found in the same geographic area, and
visually matched to the rock sample. There are similarities and
differences. The question is whether any quartzite formation is
distinctive enough physically and (or) chemically to allow it to be
used as a fingerprint for artifact sourcing, in the same way that
obsidian and chert are used. Magnification is 2.5X in both
pictures. Geochemical
techniques tested so far are INAA, ICPMS-LA, ICPMS-AD, XRF, and
flourescence. The most promising methods thusfar are ICPMS
combined with petrography. Watch for a paper in the journal
Archeology for a paper by Pitblado et al. in 2008.

NEW MEXICO MAPPING:

This
research is under the supervision of Mike Timmons at the New Mexico Bureau
of Mines and is supported by STATEMAP. Mapping emphasis is on the Carlsbad, New Mexico
area which is dominated by Permian and Tertiary bedrock. There are
also a lot of surficial units which record the history of the Pecos River.
Other mapping projects are in the Farmington area of New Mexico where the
K-T boundary is exposed.

Teepee structure in the Permian backreef of southern New Mexico--Dark
Canyon, Guadalupe Mountains.

Joel and Sienna in front of the Permian
Capitan Reef, southern New Mexico.

DEVONIAN STRATIGRAPHY OF THE GREAT BASIN:

This research is a continuation
of my Master's thesis work (Northern Arizona University). This work
focuses on the Lower and Middle Devonian strata in central Idaho, the
related vertebrate and invertebrate assemblages, and biostratigraphic/sequence
stratigraphic correlation with other Devonian strata in the Great Basin
and possibly globally. Dave Elliott (my MS advisor) and
I are looking for students to work on some of these problems. (See Dehler, 1995; Grader and Dehler, 1999)